In the field of display devices such as liquid crystal display devices and organic EL displays, in response to demands for improvements in resolution and downsizing of the devices, there has been progress in high resolution of pixels. In addition to high resolution of pixels, there are also demands for higher aperture ratios of pixels. These demands are especially noticeable in relation to high definition liquid crystal display devices with a pixel pitch of 40 μm or less.
For example, Patent document 1 proposes an active matrix liquid crystal display device whose high resolution of pixels can be achieved. Active matrix liquid crystal display devices have a configuration in which a liquid crystal layer is interposed between a TFT array substrate and an opposed substrate, where TFTs (Thin Film Transistors) are mounted on the TFT array substrate.
In the liquid crystal display devices, progress in high resolution of pixels lead to increases in wiring resistance, resulting in an increased tendency toward signal delays. Thus, to eliminate signal delays, Patent document 1 proposes a technique for forming various types of wiring including gate lines, source lines, and storage capacitor wiring from low-resistance metal materials such as aluminum (Al), copper (Cu), titanium (Ti), and silver (Ag). Hereinafter wiring made of any of these metal materials will be referred to also as metal wiring.
In liquid crystal display devices, to increase the aperture ratio of pixels, i.e., the ratio of a display area to an entire display screen, it is necessary to minimize regions serving as light-shielding portions. Also, in order to align the TFT array substrate and opposed substrate precisely, preferably the light-shielding portions are minimized. The light-shielding portions are provided on pixel boundaries, partitioning the pixels, and provided, as required, so as to cover regions where TFT and display characteristics tend to degrade.
Since the metal wiring has light-shielding properties, the technique proposed in Patent document 1 reduces light-shielding portions by not forming any additional light-shielding portion in regions that can be light-shielded by the metal wiring, and thereby reduces misalignment between the TFT array substrate and opposed substrate and improves the aperture ratio.
Also, the aperture ratio of the pixels is increased by providing an interlayer insulation layer of a special configuration on the wiring formed on the TFT array substrate and placing transparent pixel electrodes on the interlayer insulation layer.